Superconducting synchronous electric machine

ABSTRACT

The electric machine comprises a multiphase armature winding 6, a superconducting field winding 4, and a multiphase compensating winding 3 constructed in the form of sections 10. Each phase of the winding 3 is connected in series to one of the phases of the armature winding 6 through a sliding contact. The sections 10 comprise conductors of all the phases, and each phase of the winding 3 is so connected to a separate rectifier 14, 15, 16 that a unidirectional current flows therethrough.

TECHNICAL FIELD

1. Background of the Invention

The invention relates to the art of electrical engineering, andparticularly to a superconducting synchronous electric machine.

2. Background Art

Known in the art is a direct current electric machine (German acceptedpatent application No. 2,027,673, Cl. H02K 23/58, published in 1972)which is provided with a compensating winding equalizing anelectromagnetic movement of reaction of an armature, acting on asuperconducting excitation winding. The above specified electric machineprovides a principal solution to the problem of compensating thearmature reaction.

However, with varying loads on the shaft, the value of theelectromagnetic moment acting on the superconducting winding changes. Atthe same time, it is necessary to provide for a continuous control ofthe value of a current flowing through the compensating windingdepending on the value of a current within the armature winding, inorder to obtain compensation under any loading conditions. Such acontrol should be carried out in an inertialess manner since themismatch (lag and advance) of the currents within compensating andarmature windings is not permissible. Otherwise, even the instantaneousabsence of compensation of the reaction moment of the armature resultsin the failure of supports of the superconducting winding due to largemechanical loads.

Attempts have been made to solve this problem. Thus, known in the art isan electric machine (USSR Author's Certificate No. 396,792 Int. Cl. H02K19/00, Published Aug. 29, 1973) wherein the compensation of the armaturereaction moment is ensured by means of two windings which are movablewith respect to each other. In this electric machine the excitationwinding (field) consists of two windings one of which is superconductingand the other is compensating. The superconducting winding is disposedinside the rotating armature, while the other winding is located outsidethis armature. In order to compensate the armature reaction moment andto eliminate forces acting on the superconducting winding mounted in acryostat, this winding is rotatably mounted with respect to the other(compensating) winding. Under the conditions of load variations in thismachine it is necessary to ensure a corresponding change in the angle ofrotation of the superconducting winding relative to the compensatingwinding, which is accompanied by considerable performance and designdifficulties, especially because of mechanical sluggishness of thecryostat with the superconducting winding.

Also known in the art is a synchronous electric machine (USSR Author'sCertificate No. 369,659 Int. Cl. H02K 3/20, Published Feb. 8, 1973)wherein there is provided an automatic compensation of the armaturereaction moment.

The above machine comprises a field provided with a superconductingexcitation winding, a compensating winding, and a current collectingdevice comprising a commutator and brushes. A compensating device isconstructed as a distributed compensating winding which is stationarywith respect to the field structure and is provided with pairs of poleswhose number is equal to that of the machine. This compensating windingis connected in series, through the commutator and brushes fixedstationary with respect to the field, to the armature winding, the axesof phases of the compensating winding displaced relative to the axes ofphases of the armature winding by an angle of 180°. To decrease avoltage between commutator bars, the armature winding is proposed to beconnected to the compensating winding through current transformers.

In this electric machine the armature reaction flow rotates insynchronism with the field, and to compensate the above flow it isnecessary to create a rotating opposite flow of the compensatingwinding. In the considered machine the compensating winding which isstationary relative to the armature is formed by means of the commutatorand brushing device. The latter forms a required number of phases fromthe total number of turns of the collector winding. In the process ofrotation of the field with the compensating winding disposed thereon,the brushing device is stationary relative to the armature winding, thephases of the compensating winding disposed therebetween being alsostationary. The composition of winding sections included into each phaseis continuously changing. Power supply of the compensating winding withalternating current is ensured by the magnetic flow rotating relative tothe armature winding and stationary with respect to the field structure.The function of the commutator and brushing device in this synchronousmachine consists in switching the winding turns and forming phases ofthe compensating winding in contrast to the function of a rectifier inthe direct current machine.

Closing the circuits of phases of the armature winding through thecircuits of the compensating winding requires the availability ofspecial sensitive protection instrumentation in the circuit of eachphase of the armature winding for the case of open- or short-circuit inany section of the compensating winding. Open or short circuit does notresult in breaking the armature winding circuit, though in this case thefield of the compensating winding is distorted and its magnitude isdecreased, which is inadmissible. The presence of the brushing deviceand commutator and their operation from an alternating current powersupply results in further complication of the machine and reducesreliability thereof.

Feeding the compensating winding through current transformers for thepurpose of decreasing the voltage between the commutator bars isinadmissible since the presence of transformers in the feeding circuitsof the compensating winding leads to the lag of changing thecompensating field following the change in the armature field due to theelectrical inertia of the current transformers. All this results incomplication of both the machine and its maintenance, and consequentlyin a decrease in its performance reliability.

SUMMARY OF THE INVENTION

The invention is based on the problem to provide a synchronous electricmachine whose performance reliability would be upgraded due to improvingthe design of the compensating winding and power supply means thereof.

The object set forth is attained in a synchronous electric machine,comprising a multiphase armature winding a superconducting field, and amultiphase compensating winding made in the form of sections, each phaseof the compensating winding being connected in series through a slidingcontact to one of the phases of the armature winding, according to theinvention each section of the compensating winding comprises conductorsof all the phases, and each phase of the compensating winding isconnected to a separate rectifier so that a unidirectional current wouldflow therethrough.

The provision of each section of the compensating winding from acombination of conductors of all the phases, separate feeding thereofthrough the rectifiers, and series connection thereof into the phases ofthe armature winding ensures the total current of a composite conductorof the section being constant and proportional to the armature currentat any instant of time and provides an inertialess and automaticcompensation of reaction movement of the armature.

Such connection of the phases of the compensating and armature windingsensures the flow of the same current therethrough, therefore anyemergency variation of parameters of any of these windings causes achange in the current flowing therethrough.

Thus, the system used for the armature protection simultaneouslyprotects the compensating winding thereby eliminating the need ofadditional devices for the protection of the latter. The absence of asection commutator and a phase former of the compensating winding, i.e.an alternating current operated collector, results in the simplificationof the machine and in an increase in the performance reliabilitythereof.

It is advantageous to construct the claimed synchronous electric machineso that each phase of the compensating winding be divided into twobranches connected antiparallel therebetween and connected to separaterectifiers.

Such a design is the most suitable for low-voltage machines since itallows the number of rectifier components to be reduced, therebyupgrading reliability of such machines.

In high-power machines it is reasonable to transpose the conductors ofdifferent phases of the compensating winding therebetween.

In the above specified group of machines in the case where thedimensions of a conductor of the compensating winding become comparablewith the distance between the compensating winding and the fieldwinding, the location of conductors of different phases within thesection of the compensating winding influences the form of acompensating field, and consequently the compensating moment. At thesame time, the above described arrangement of the compensating windingallows the distortions of the form of a compensating field to bereduced.

It is rather convenient to utilize reversible rectifiers in the claimedsynchronous electric machine, by means of which the phases of thecompensating winding are connected in series to the circuits of thephases of the armature windings, and to mount a sign-sensitive torquetransducer on the armature shaft, the output of said transducer beingconnected to an input of a control device which is electrically coupledto said reversible rectifiers.

BRIEF DESCRIPTION OF DRAWINGS

The invention is further explained in greater detail in terms ofspecific embodiments thereof with reference to the accompanyingdrawings, in which:

FIG. 1 shows a longitudinal section of a portion of the inventivesynchronous electric machine;

FIG. 2 shows an embodiment of a section of the compensating winding ofthe claimed synchronous electric machine;

FIG. 3 shows a modification of a connection diagram of adjacent sectionsof the compensating winding, of which one is illustrated in FIG. 2;

FIG. 4 shows a connection diagram of the armature winding, compensatingwinding, and rectifiers of the claimed synchronous electric machine;

FIG. 5 shows another modification of the diagram shown in FIG. 4,utilized for low-voltage machines, of the invention;

FIG. 6 shows a modification of the diagram illustrated in FIG. 4,utilized in the reversal of the claimed synchronous electric machine;and

FIG. 7 shows the law of current time variation in the compensatingwinding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A synchronous electric machine comprises a stator 1 (FIG. 1) on whichthere are mounted a cryostat 2 and a compensating winding 3. Inside thecryostat 2 are located a super-conducting field winding 4 and arotatable armature 5 provided with a multiphase winding 6 which isconnected to a rectifying device 9 and the compensating winding 3through contact rings 7 and brushes 8. The compensating winding 3 isfixed on the stator 1 and is at a normal temperature.

A section 10 (FIG. 2) of the compensating winding 3 is a combination ofconductors 11, 12, 13 of different phases. For instance, the conductor11 is connected to a phase A, the conductor 12, into a phase B, and theconductor 13, into a phase C. As shown in FIG. 2, the section 10 isprovided with a bend in the front portion thereof. Such a transpositionof conductors can be adequate in the case where the dimensions of thesection 10 are commensurate with a distance between the compensatingwinding 3 and the field winding 4. For high power machines thetransposition of the phase conductors 11, 12, 13 within a slot portionof the section 10 may be expedient.

Starting and end points of the phase conductors 11, 12, 13 (FIG. 3) areconnected either in series under high voltage supply of the machine orin parallel under low voltage. The conductors 11 of all the sections ofthe compensating winding 3 form the phase A of this winding, theconductors 12, the phase B, and the conductors 13, the phase C.

In the preferred embodiment of the invention the rectifying device 9 iscomposed of three rectifying bridge circuits 14, 15, 16 (FIG. 4), one ofthe phases A, B, C of the compensating winding 3 being connected to thediagonal of each of said circuits.

To reduce the number of components of the rectifying device 9, in lowvoltage machines each phase of the compensating winding 3 can be dividedinto two branches 17, 18 (FIG. 5) which are connected anti-parallel toseparate rectifiers 19, 20.

In the case of changing the sign of the electromagnetic moment of thearmature, (e.g. when reversing the motor), the sign of the compensatingelectromagnetic moment must be changed as well, for which purpose thedirection of current within the compensating winding is to be changedfor the opposite.

According to one embodiment of the invention, this is attained byproviding reversible rectifying bridge circuits 14, 15, 16. Aconventional reversible converter 21 can be used as such reversiblerectifying bridge circuit, the legs of said circuit being formed bythyristors connected anti-parallel. The above converters can becontrolled by means of a suitable conventional control device 22 whichare widely applied in the industry. The input of the device is connectedto the output of a sign-sensitive transducer 23 of the torque, saidtransducer being mounted on the armature shaft 24. The sign-sensitivetransducer 23 of the torque may be a transducer of a conventionaldesign, which is a magnetoelastic circular torsiometer whose operationis based on the measurement of variations in the magnetic permeabilityof ferromagnetic bodies depending on mechanical stresses appearing underthe action of the applied forces.

The synchronous electric machine operates as follows.

In the process of operation of the machine there appears anelectromagnetic moment of the armature reaction, said moment acting onthe field winding 4. The compensating winding 3 creates a moment actingon the field winding 4 and compensating a moment of the current flowingin the winding 6 of the armature. Rectified half-waves of phase currentsi_(A) --i'_(A), i_(B) --i'_(B), i_(C) --i'_(C) (FIG. 7) flow througheach of the phase conductors 11, 12, 13 of the compensating winding 3,said half-waves being shifted in time. The total current within thesection of the compensating winding 3 is equal to the sum of currents ofthe phase conductors and has a constant value with an average magnitudeof I_(o). The value I_(o) varies corresponding to the changes in thephase currents of the armature reaction moment under variable loads.

In the case where the connection of the compensating winding is carriedout as illustrated in FIG. 5, half-waves of respective phase currents ofthe armature winding flow through each parallel branch of the phase ofthe compensating winding, said half-waves having different directions,but due to the opposing connection of said branches the total current ofthe composite phase conductor maintains the same direction and magnitudeas in the above described case.

When reversing the machine, the reaction moment of the armature changesits sign for the opposite, which leads to the necessity of changing thesign of the compensating momentum created by the compensating winding 3.To accomplish this condition it is necessary to change the directions ofcurrents of the phases of the compensating winding. Such a change isensured by one embodiment of the invention, wherein the phases of thecompensating winding are fed through the reversible converters 21 whichensure a required direction of the current flowing through thecompensating winding 3 depending on the direction of the effect of theelectromagnetic moment of the armature. The control of the converters 21is accomplished by means of the control device 22 converting a signalproduced by the sign-sensitive transducer 23 of the torque.

The claimed electric machine including an improved design of thecompensating winding allows the maintenance thereof to be simplified andthe operation reliability to be upgraded.

INDUSTRIAL APPLICABILITY

The invention can be used when providing and developing superconductingsynchronous high- and medium power electric machines.

The invention is the most expedient to be utilized as an electric motorin the drives which are characterized by quick-changing loads.

We claim:
 1. A superconducting synchronous electric machine, comprisinga multiphase armature winding supported on an armature which, in turn,is supported on an armature shaft, a superconducting field winding, anda compensating winding constructed in the form of sections, thecompensating winding being connected in series to the armature windingthrough a sliding contact, characterized in that the compensatingwinding (3) is made multiphase, sections (10) thereof compriseconductors (11, 12, 13) of all the phases, and each phase of thecompensating winding (3) is so connected to a separate rectifier (14,15, 16) that a unidirectional current flows therethrough and furthercomprising a sign-sensitive transducer mounted on said armature shaft.2. A synchronous electric machine as claimed in claim 1, characterizedin that each phase of the compensating winding (3) is divided into twobranches (17, 18) connected to separate rectifiers (19, 20), saidbranches being connected anti-parallel therebetween.
 3. A synchronouselectric machine as claimed in claims 1 or 2, characterized in thatconductors of different phases of the compensating winding (3) aretransported therebetween.
 4. A synchronous electric machine as claimedin claim 1 characterized in that it utilizes reversible rectifiers (21)by means of which the phases of the compensating winding are connectedin series to the circuits of phases of the armature winding (6), theoutput of said transducer being connected to the input of a controldevice (22), electrically connected with said reversible rectifiers(21).
 5. A synchronous electric machine as claimed in claim 2,characterized in that it utilizes reversible rectifiers (21) by means ofwhich the phases of the compensating winding are connected in series tothe circuits of phases of the armature winding (6), the output of saidtransducer being connected to the input of a control device (22),electrically connected with said reversible rectifiers (21).
 6. Asynchronous electric machine as claimed in claim 3, characterized inthat it utilizes reversible rectifiers (21) by means of which the phasesof the compensating winding are connected in series to the circuits ofphases of the armature winding (6), the output of said transducer beingconnected to the input of a control device (22), electrically connectedwith said reversible rectifiers (21).